A mine closure provision is a real number on a real balance sheet — the money set aside to rehabilitate the site one day. That number is built on two physical measurements: how much ground has been disturbed, and how much earth has to be moved to put it right. Both usually come from the parties with an interest in their size. An independent measurement from satellite and elevation data is the check that the figure the auditor signs off is the figure the ground supports.
What the provision is actually made of
Strip a closure-cost estimate back and the money sits downstream of two quantities. Disturbed area — hectares of footprint to be reshaped, capped and revegetated — drives the per-hectare rehabilitation cost. Earthworks volume — cubic metres of spoil, tailings or overburden to be moved, reshaped or hauled — drives the per-cubic-metre earthmoving cost. Get either quantity wrong and the provision is wrong by the same proportion, no matter how carefully the unit rates were built. The financial question is, at its root, two measurement questions.
Measuring the disturbed area — from the archive, at many dates
The extent of disturbance is exactly what the optical satellite archive is good at. Sentinel-2 and the longer Landsat record let the footprint be mapped, not estimated from a walk-around or a single plan — bare ground, tailings, pit and infrastructure separated from surrounding land by their spectral signature, at 10-metre resolution and every few days. Because the archive is historical, the footprint can be measured at several dates: how it grew, when, and by how much. A provision that has to describe a footprint's whole life is then resting on a measured trajectory, not a present-day snapshot with the past filled in by assumption.
Measuring the volume — differencing two surfaces
Volume is a harder measurement, and it's worth being precise about how it's done and what it needs. You quantify how much earth has moved by comparing two elevation surfaces (digital elevation models) of the same ground at different times, and integrating the height difference over the area — a "DEM of difference." Where the later surface is lower, material was removed; where higher, it was placed. The volume is the sum of those differences across the footprint.
The honest part is where the elevation data comes from. Free optical imagery gives you area, not height — so a defensible volume needs elevation surfaces from stereo satellite, airborne LiDAR, drone photogrammetry, or an archival survey, chosen to match the site and the era being measured. Each surface carries a vertical uncertainty, and those errors propagate into the volume figure: a small height error over a large area is a large cubic-metre error. A volume reported without a stated uncertainty, or without saying which surfaces it came from, is a number without a pedigree — and a closure figure is exactly the place that pedigree gets tested.
Verifying a number someone else already produced
Often the quantities already exist — a surveyor or contractor has stated them. Independent measurement then does something quietly valuable: it checks those figures against the satellite and elevation record and reports the agreement, or the discrepancy, with its basis shown. For an auditor testing a provision, or a consultancy reviewing a number it didn't generate, that is an evidence trail instead of a quantity taken on trust from the party it flatters.
Where the line sits
TerraX signs the measurement — disturbed area, earthworks volume, the imagery and elevation basis for each, and the uncertainty on both. It does not opine on whether a provision is adequate, design the closure, or decide the accounting treatment of the liability: those judgements sit with appropriately registered engineers, environmental assessment practitioners and financial professionals, and where a scope needs them they are brought in. A verification is more credible, not less, for being clear about where its authority ends.
The value is independence: a source for the numbers under the provision that does not report to the operation whose liability they describe. That's what our closure liability verification service delivers — tell us the site and whether quantities already exist, and we'll measure them against the record.